1. Field of the Invention
The present invention is generally concerned with printing machines of the kind using a turntable rotatable about an axis perpendicular to its plane and to which a plurality of spaced object supports are attached in a circular arrangement.
It is more particularly, although not necessarily exclusively, directed to the situation in which flat objects such as disks must be printed on a plane surface perpendicular to the rotation axis of the turntable.
2. Description of the Prior Art
The object supports currently used are attached directly to the turntable.
If there is a suction head under each object support for holding the supported object there is merely a seal between each support and the turntable.
The suction head is attached to the turntable.
In the case of printing in more than one color the diameter of the turntable is proportional to the number of colors to be printed because as many printing heads and curing ovens are required on the path of the object supports as there are colors to be applied.
Given the inevitable machining tolerances it is then extremely difficult, if not impossible, to achieve sufficient flatness of the turntable perpendicular to its rotation axis, by which is meant a flatness within tolerances closer than 0.2 mm.
Consequently, the level of the printing surface is not strictly identical for all the object supports as they are fed under a printing head but to the contrary may vary from one object support to the next all around the turntable.
In the case of silkscreen printing of simple designs in only one color the pressure exerted by the squeegee on the screen and therefore through the screen on the objects to be printed is usually sufficient to compensate for these slight departures of the turntable from perfect flatness, given the capacity for deformation of the screen.
Thus in practise these defects are of no consequence in this case.
The same cannot be said in respect of multicolor printing.
In this case the various transparent colors employed must be printed one on top of the other.
The pressure of the squeegee depends on their thickness and therefore on their color intensity.
To obtain the same shade reliably for all the printed objects it is essential for the squeegee pressure to be the same from one object support to the next. In other words, the respective printing surfaces must be at exactly the same level relative to the path of the squeegee for all the object supports.
A general object of the present invention is an arrangement whereby this requirement can be satisfied in a simple and reliable manner.